Start with the right checks.
No power, an error screen and a restart loop need different investigations. The useful first job is identifying which one you have. A photo of the exact screen can be more useful than calling every startup problem a crash.
What to do next.
Check the power connection and note whether lights, fans or a manufacturer logo appear.
Record the exact error or repeated screen. Include whether the issue followed an update or hardware change.
Disconnect an unnecessary external accessory only when it is safe to do so. Keep the normal keyboard, screen and power arrangement simple.
Review Microsoft’s recovery options from another device, starting with the least disruptive option appropriate to the symptom. Ask for guidance if the effect on files is unclear.
Check the result.
If Windows starts, make a recovery copy of important work and check the original failing task. Keep the error information in case the issue returns.
Stop and get help if…
The drive makes unusual noises, the PC has physical damage or recovery asks to erase the only copy of your files. Remote assistance may help assess next steps, but physical hardware work can need separate service.